“Here are the Bach pieces. They’re fairly old, I haven’t looked at them in several years. Still, I’m almost sure…” She lapsed into silence, flipping quickly through the pages of the Bach scripts on her knee, one at a time, glancing back now and then at the “Lied” on the rack.

“Ha!” she let out a cry of triumph, and held out one of the Bach pieces to me. “See there?”

The paper was titled “Goldberg Variations,” in a crabbed, smeared hand. I touched the paper with some awe, swallowed hard, and looked back at the “Lied.” It took only a moment’s comparison to see what she meant.

“You’re right, it’s the same!” I said. “A note different here and there, but basically it’s exactly the same as the original theme of the Bach piece. How very peculiar!”

“Isn’t it?” she said, in tones of deep satisfaction. “Now, why is this anonymous composer stealing melodies and treating them in such an odd fashion?”

This was clearly a rhetorical question, and I didn’t bother with an answer, but asked one of my own.

“Is Bach’s music much in vogue these days, Mother?” I certainly hadn’t heard any at the musical salons I attended.

“No,” she said, shaking her head as she peered at the music. “Herr Bach is not well known in France; I believe he had some small popularity in Germany and in Austria fifteen or twenty years ago, but even there his music is not performed much publicly. I am afraid his music is not the sort to endure; clever, but no heart. Hmph. Now, see here?” The blunt forefinger tapped here, and here, and here, turning pages rapidly.

“He has repeated the same melody – almost – but changed the key each time. I think this is perhaps what attracted your husband’s notice; it is obvious even to someone who doesn’t read music, because of the changing signatures – the note tonique.”

It was; each key change was marked by a double vertical line followed by a new treble clef sign and the signature of sharps or flats.

“Five key changes in such a short piece,” she said, tapping the last one again for emphasis. “And changes that make no sense at all, in terms of music. Look, the basic line is precisely the same, yet we move from the key of two flats, which is B-flat major, to A-major, with three sharps. Stranger yet, now he goes to a signature of two sharps, and yet he uses the G-sharp accidental!”

“How very peculiar,” I said. Adding a G-sharp accidental to the section in D-major had the effect of making the musical line identical with the A-major section. In other words, there was no reason whatsoever to have changed the key signature.

“I don’t know German,” I said. “Can you read the words, Mother?”

She nodded, the folds of her black veil rustling with the movement, small eyes intent on the manuscript.

“What truly execrable lyrics!” she murmured to herself. “Not that one expects great poetry from Germans in general, but really… still-” She broke off with a shake of her veil. “We must assume that if your husband is correct in assuming this to be a cipher of some sort, that the message lies embedded in these words. They may therefore not be of great import in themselves.”

“What does it say?” I asked.

“ ‘My shepherdess frolics with her lambs among the verdant hills,’ ” she read. “Horrible grammar, though of course liberties are often taken in writing songs, if the lyricist insists upon the lines rhyming, which they nearly always do if it is a love song.”

“You know a lot about love songs?” I asked curiously. Full of surprises tonight, was Mother Hildegarde.

“Any piece of good music is in essence a love song,” she replied matter-of-factly. “But as for what you mean – yes, I have seen a great many. When I was a young girl” – she flashed her large white teeth in a smile, acknowledging the difficulty of imagining her as a child – “I was something of a prodigy, you understand. I could play from memory anything I heard, and I wrote my first composition at the age of seven.” She gestured at the harpsichord, the rich veneer shining with polish.

“My family has wealth; had I been a man, no doubt I would have been a musician.” She spoke simply, with no trace of regret.

“Surely you could still have composed music, if you’d married?” I asked curiously.

Mother Hildegarde spread her hands, grotesque in the lamplight. I had seen those hands wrench loose a dagger embedded in bone, guide a displaced joint back into alignment, cup the blood-smeared head of a child emerging from between its mother’s thighs. And I had seen those fingers linger on the ebony keys with the delicacy of moths’ feet.

“Well,” she said, after a moment’s contemplation, “it is the fault of St. Anselm.”

“It is?”

She grinned at my expression, her ugly face quite transformed from its stern public facade.

“Oh, yes. My godfather – the Old Sun King,” she added casually, “gave to me a book of the Lives of the Saints for my own Saint’s Day when I was eight. It was a beautiful book,” she said reminiscently, “with gilded pages and a jeweled cover; intended more as a work of art than a work of literature. Still, I read it. And while I enjoyed all of the stories – particularly those of the martyrs – still there was one phrase in the story of St. Anselm that seemed to strike a response in my soul.”

She closed her eyes and tilted back her head, recalling.

“St. Anselm was a man of great wisdom and great learning, a Doctor of the Church. But also a bishop, a man who cared for the people of his flock, and looked after their temporal needs as well as those of the spirit. The story detailed all of his works, and then concluded in these words – ‘And so he died, at the conclusion of an eminently useful life, and thus obtained his crown in Paradise.’ ” She paused, flexing her hands lightly on her knees.

“There was something about that that appealed most strongly to me. ‘An eminently useful life.’ ” She smiled at me. “I could think of many worse epitaphs than that, milady.” She spread her hands suddenly and shrugged, an oddly graceful gesture.

“I wished to be useful,” she said. Then, dismissing idle conversation, she turned abruptly back to the music on the rack.

“So,” she said. “Plainly the change in the key signatures – the note tonique – that is the oddity. Where can we go with that?”

My mouth dropped open with a small exclamation. Speaking in French as we had been, I hadn’t noticed before. But observing Mother Hildegarde as she told her story, I had been thinking in English, and when I glanced back at the music it hit me.

“What is it?” the nun asked. “You have thought of something?”

“The key!” I said, half-laughing. “In French, a musical key is the note tonique, but the word for an object that unlocks…” I pointed to the large bunch of keys – normally carried on her girdle – that Mother Hildegarde had laid aside on the bookshelf when we came in. “That is a passe-partout, isn’t it?”

“Yes,” she said, watching me in puzzlement. She touched the skeleton key in turn. “Une passe-partout. That one,” she said, pointing to a key with barrel and wards, “is more likely called a clef.”

“A clef!” I exclaimed joyously. “Perfect!” I stabbed a finger at the sheet of music before us. “See, ma mere, in English, the words are the same. A ‘key’ gives the basis of a piece of music, and a ‘key’ unlocks. In French, the clef is a key, and in English, the ‘clef’ is also part of the musical signature. And the key of the music is also the key to the cipher. Jamie said he thought it was an English cipher! Made by an Englishman with a really diabolical sense of humor, too,” I added.

With that small insight, the cipher proved not too difficult to unravel. If the maker was English, the ciphered message likely was in English, too, which meant that the German words were provided only as a source of letters. And having seen Jamie’s earlier efforts with alphabets and shifting letters, it took only a few tries to determine the pattern of the cipher.